Emergency life support unit

ABSTRACT

A hood for providing a user with breathable air having CO 2  absorption means disposed therein, in which the absorption means is intimately admixed with a fibrous material.

This application is a continuation of application Ser. No. 07/498,442filed Mar. 22, 1990 which is a continuation of Ser. No. 07/228,060 filedAug. 4, 1988, both now abandoned.

BACKGROUND OF THE INVENTION

A wide variety of emergency breathing equipment has previously beendeveloped, such as the protective hood with CO₂ absorbant described inWerjefelt, U.S. Pat. No. 4,627,431, and the multilayered hood withelastomeric neck seal described in copending, coassigned U.S.application Ser. No. 120,533, filed Nov. 13, 1987. This type ofequipment generally includes a protective hood, a source of oxygen and ameans to remove, from the hood interior, the carbon dioxide exhaled bythe wearer.

Lithium hydroxide (LiOH) is one compound commonly used to absorb thecarbon dioxide. LiOH is often preferred as an absorbent because itprovides acceptable absorption characteristics with acceptable weight.Particularly in aircraft applications, weight is an importantconsideration.

Lithium hydroxide is readily available in powder form, which provides asurface area that maximizes its effectiveness as an absorbant. However,the powder dust is a respiratory irritant, and should therefore beisolated from the wearer.

Previously, scrubbers were constructed by impregnating felt with LiOHpowder by putting the two together in a ball mill. The resulting loadedfelt was encased in an envelope of semipermeable membrane that allowedgas flow through the envelope while retaining the LiOH. Heat sealing ofsuch envelopes was also used to maintain the uniform distribution of theLiOH powder within the envelopes.

While such previous techniques and designs were satisfactory, continuingeffort has been devoted to a CO₂ absorbant system that would provideimproved balance among maximum absorption, isolation from the wearer,ease of manufacture and low cost and weight.

SUMMARY OF THE INVENTION

The present invention provides a protective hood having a CO₂ absorbantwhich is easily and economically manufactured, and provides uniformdistribution of absorbant, excellent absorption capability and isolationof the absorbant from the user.

Specifically, the present invention provides, in a protective hood forproviding a user with breathable air which envelopes at least the headof the user and contains CO₂ absorption means disposed inside the hood,the improvement wherein the CO₂ absorption means is uniformly admixedwith about from 0.1 to 70%, by weight of the mixture, of a fibrousmaterial, and the CO₂ absorption means is disposed in the form of asheet having a thickness of about from 1 to 25 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a protective hood of the presentinvention, partly cut away to show the CO₂ absorption means disposedinside the hood.

FIG. 2 is a perspective view of another embodiment of the presentinvention.

FIG. 3 is a cross-sectional view of the preferred CO₂ absorption meansused in the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The protective hoods of the present invention can be constructedaccording to the general configuration, and with the materials specifiedin, the aforementioned Werjefelt, U.S. Pat. No. 4,627,431, andcopending, coassigned U.S. application Ser. No. 120,533, filed Nov. 13,1987, both of which are hereby incorporated by reference.

The present invention resides in the provision of a CO₂ absorption meanswhich is compounded with a fibrous material, to uniformly and intimatelyadmix the absorption means with the fibrous material. This compoundingstabilizes the CO₂ absorption means, reducing dusting and thepossibility of irritation of the user. A wide range of compositions ofthe CO₂ absorption means and the fibrous material can be used, in thatthe fibrous material can comprise about from 0.1 to 70% by weight of themixture. Preferably, the fibrous material comprises about from 0.5 to50% by weight of the mixture, and especially about from 1 to 10%.

CO₂ absorption means which can be used in the present invention includealkali and alkaline earth metal hydroxides and oxides, such as calciumhydroxide, calcium oxide, sodium hydroxide and barium hydroxide. Ofthese, the lithium and sodium salts are preferred, and lithium hydroxideis particularly preferred. In general, for the best balance of handingand absorption characteristics, lithium hydroxide having a particle sizeof about from 5 to 250 microns is used.

The CO₂ absorption means is admixed, or compounded, with any fibrousmaterial that can be laid down in a mat or sheet by wet or drytechniques. Fibrous materials which can be used include polymeric fiberssuch as polyolefins, polyesters, and polyamides with fiber lengths inthe range of about from 0.1 to 3 inches. Inorganic fibers can also beused.

Fibrous materials which are preferred in the present invention arefluorocarbons, such as polytetrafluoroethylene. That commerciallyavailable from E. I. du Pont de Nemours and Co. as "Teflon TFE3512",when formed into fibrids, has been found to be particularlysatisfactory. Other fluorocarbons which can be used include thatcommercially available from E. I. du Pont de Nemours and Co. as TeflonK10 fluoropolymer. A preferred polypropylene which can be used is thatcommercially available from E. I. du Pont de Nemours and Co. in the formof polypropylene fibrids as "Pulp Plus."

The fibrous material can either be used in a fibrilated form or it canbe simultaneously fibrilated and compounded with the CO₂ absorbant.While the use of prefibrilated material, such as the polypropylenefibrids noted above, is satisfactory, it is preferred to simultaneouslyfibrilate the material and compound it with the CO₂ absorption means.This simultaneous fibrilation and compounding results in a greaterdegree of encapsulation of the absorbant, and a more stable structure.

After compounding of the CO₂ absorption means with the fibrous material,it is cast into sheet form. Generally, the compounded material isdispersed in a fluid to facilitate casting. Fluids which can be usedinclude any that do not dissolve the fibrous material or the CO₂absorption means under the conditions used, such as aliphatic andaromatic hydrocarbon solvents. Naptha, however, is a preferreddispersion aid. The dispersion can be cast into sheet form usingconventional paper-making techniques.

In the alternative, the compounded CO₂ absorption means can bepelletized and incorporated into a sheet structure by dry techniques.For example, the pellitized CO₂ absorption means can be spread betweentwo sheets of permeable membrane and then needle-punched for structuralintegrity.

Regardless of whether a wet or dry preparation method is used, theabsorbant and the fibrous material in the sheets of CO₂ absorption meansare uniformly admixed. For example, in a four square inch sheet of theabsorption means, the relative concentration of the absorbant and thefibrous material will generally not vary more than about 20% by volume.

It is preferred that a CO₂ permeable membrane be bonded to at least onesurface of the compounded CO₂ absorption means, and especially to bothsurfaces. It has been found that these layers improve the overallstrength of the absorbant structure. A wide variety of membranes can beused, so long as the membrane does not significantly inhibit air flowthrough the absorbant. The fabric preferably has a pore size of at leastabout 0.1 micron. A particularly satisfactory material is thatcommercially available from E. I. du Pont de Nemours and Co. as Nomexhydrolaced fabric.

The membrane or fabric can be applied to the compounded CO₂ absorptionmeans before or after formation of the sheet. For example, the absorbantsheet can be cast onto a layer of permeable fabric from a dispersion.

The CO₂ absorbant sheet is preferably treated to impart threedimensional integrity. Ultrasonic bonding, heat bonding, stitching orhydrolacing with an appropriate liquid can be so used to advantage.However, needling with conventional apparatus such as a needleloom, usedfor felting, is preferred for such treatment.

In the preferred manufacturing techniques used in the present invention,LiOH powder is combined with a high-fibrillating fluoropolymer in a highshear mixer which results in a dustless mass of material. This mass isdispersed in non-solvent using a high shear mixer and the slurry isdeposited onto a permeable sheet using traditional paper makingequipment. The resulting sheet is dried and a second permeable sheet isput on top and the entire sandwich is mechanically needled using aneedleloom.

The hoods of the present invention can have the tubular configurationshown in U.S. Pat. No. 4,627,431, with a substantially circular topsection attached to a tubular side section. Such a configuration is showin FIG. 1, in which generally tubular portion 1, having upper end 2 andlower end 3, has a continuous sidewall which forms the basic componentof the hood. The upper end of the tubular portion is bonded to circulartop portion 5. Substantially annular resilient neck seal 6 is attachedto the inner side portion of the lower end of the tubular portion, theneck seal having an opening 7 for admitting at least the head of theuser to form a closure around the user. CO₂ absorption means 8 isencased in envelopes 9 and attached to the interior sidewall of thetubular portion of the hood. If external air sources are intended to beused for the hood, the construction preferably further comprises inflowvalve 10 and outflow valve 11.

Alternatively, the hoods of the present invention can be constructedwith a single piece of material, as shown in FIG. 2. There, the closedupper end of the hood 22 is formed by a folded configuration similar tothe bottom of a paper bag. This embodiment is preferred for ease ofconstruction.

In FIG. 3, the preferred construction of the CO₂ absorption means isshown. There, the absorbant 31 is intimately admixed with fibrousmaterial 32, and disposed in the form of a sheet. Permeable fabriclayers 33 and 34 are bonded to each surface of the admixed absorbant andfibrous material.

The compounding of the absorbant with the fibrous component, inaccordance with the present invention, substantially reduces theproblems associated with dust from the absorbant. The use of papermaking techniques allows a uniform distribution of the absorbant withinthe resultant structure. The layers of fibrous sheet, and especially thepreferred materials, add strength and fire resistance. The preferredmechanical treatment insures long term scrubber mechanical integrity andprevents substantial migration or settling of LiOH powder in thescrubber. Since the absorbant is so effectively bound by the fibrousmaterial and the mechanical treatment, the costly envelopes of expandedpolytetrafluoroethylene are no longer required. Instead, the sandwichcan be inserted into a permeable envelope of sufficient strength for theintended use and inserted into the hood.

The present invention is further illustrated in the following specificexample.

EXAMPLE

60 grams of environmental grade anhydrous LiOH powder (6-14 Tyler mesh)was ground to a particle size of about 10 microns in a hammer mill. TheLiOH was mixed with polytetrafluoroethylene (TFE) powder (commerciallyavailable from E. I. du Pont de Nemours and Co. as "Teflon TFE3512") ina ratio of 98% LiOH, 2% Teflon by weight, at 212 degrees F. for oneminute in a high shear Banbury mixer. The resultant mass of material wasdispersed in one quart of a hydrocarbon liquid (VM&P Naptha) using aWaring blender and blended to uniformity. The mixture was furtherdiluted with VM&P Naptha to a final quantity of about 3 gallons withstirring adequate to maintain a uniform dispersion.

A 0.9 ounce/square yard, 12"×12" sheet of permeable fabric (commerciallyavailable from E. I. du Pont de Nemours and Co. as Nomex spunlacedfabric) was laid onto the screen of a laboratory size paper makingmachine. The LiOH/Teflon/Naptha slurry was poured in to provide aneffective LiOH loading of 60 grams/sq. ft. 15" of mercury vacuum wasapplied and then the 2 layer structure was pressed at 60 psi. Theresulting paper was dried at 230° F. for one hour. Finally, a second 0.9oz./sq. yd., 12"×12" sheet of spunlaced fabric was added and the entirestructure was needled on a Dilo needleloom. Several identical compositesheets were made as described above, pieced together and cut as required(using an industrial-type sewing machine) to form five individualpieces; one about 6"×12, two about 6"×24" and two about 18"×4" Thecomposite sheets were then incorporated into individual 2-layermelt-blown polypropylene envelopes (outer layer 35 grams/square meter,inner layer 20 grams/square meter). The envelope is formed usingtraditional sewing techniques. Buttonholes were included for ease ofattachment in a smoke hood, and additional stitching lines were added toaid folding these scrubbers and placement within the hood.

Emergency life support hoods incorporating the scrubbers were tested,and passed the tests for aircraft crewmembers described in the FAAaction notice, A8150.2 of Sep. 1, 1987. The tests model the workload ofan aircraft crewmember while putting out an on-board fire.

I claim:
 1. In a protective hood for providing a user with breathableair which envelopes at least the head of the user and contains CO₂adsorption means disposed inside the hood, the improvement wherein theCO₂ adsorption means is uniformly admixed with about from 0.1 to 70% byweight of the mixture, of a fibrous material, and the CO₂ adsorptionmeans is disposed in the form of a sheet having a thickness of aboutfrom 1 to 10 mm, the CO₂ adsorption means having been prepared bysimultaneously fibrilating fluorocarbon resin and compounding with CO₂absorbant with a high shear mixer dispersing the resulting compoundedCO₂ adsorption means in a fluid which is a non-solvent for both thefibrous material and the CO₂ adsorption means, and casting thedispersion into sheet form and removing the non-solvent.
 2. A protectivehood of claim 1 wherein the sheet has a permeable fabric bonded to atleast one surface thereof, the membrane having a pore size of at leastabout 0.1 micron.
 3. A protective hood of claim 2 wherein the sheet hasa permeable fabric bonded to both surfaces of the sheet.
 4. A protectivehood of claim 3 wherein the permeable fabric consists essentially ofpolyamide spunlaced fabric.
 5. A protective hood of claim 3 wherein thepermeable fabric consists essentially of polyester spunlaced fabric. 6.A protective hood of claim 3 wherein the permeable fabric consistsessentially of polytetrafluoroethylene.
 7. A protective hood of claim 1wherein the CO₂ absorption means is selected from the group consistingof alkali and alkaline earth metal oxides and hydroxides.
 8. Aprotective hood of claim 7 wherein the CO₂ absorption means consistsessentially of lithium hydroxide.
 9. A protective hood of claim 1wherein the fibrous material consists essentially ofpolytetrafluoroethylene.
 10. A protective hood of claim 7 wherein thefibrous material has a fiber length of about from 1/8 to 11/2 inch. 11.A protective hood of claim 1 wherein the sheet has been mechanicallytreated to improve the stability of the absorbant in the fibrousmaterial.